In the past, a cable had been frequently used as a medium for transmitting electrical energy, but, recently, a bus bar, having an advantage of transmitting a larger amount of electrical energy by the same volume of conductor, has been widely used as an alternative to a cable. Such a bus bar must have excellent electrical conductivity, high strength and excellent durability.
A bus bar is used in large industrial distribution boards or switchboards requiring the installation of a large-capacity electrical energy transmitting system as well as in small household distribution boards or switchboards. Such a bus bar is generally composed of a copper bar, and thus its thickness is changed depending on current capacity.
Since copper, which is a main raw material of a bus bar, mostly depends on import, it is sensitive to foreign copper prices. The price of copper is greatly changed every year, and the change in import price of copper is also increased, thus increasing the cost of manufacturing a bus bar.
Recently, in order to solve such a problem by reducing cost, decreasing weight and improving performance, a composite bus bar, which is formed by coating aluminum with copper or by coating an iron alloy with copper, has entered the market.
Such a composite bus bar is currently manufactured by clad bonding, hydrostatic extrusion or indirect extrusion. In clad bonding, a composite bus bar is manufactured by rolling two or more metal materials at high temperature to bond them together. In both hydrostatic extrusion and indirect extrusion, a layered composite bus bar is manufactured by inserting a billet having a predetermined shape into an extrusion container.
However, the clad bonding method is problematic in that the rolling of metal materials is generally performed at high temperatures, but metal materials, such as copper, iron and the like, are oxidized at a low temperature of 200° C. or lower, and the thermal expansion rates thereof are different from each other, so these metal materials are not suitably bonded, thereby producing defective products in large quantity. Further, this clad bonding method is problematic in that manufacturing processes and equipment are complicated, thus increasing a production cost.
Meanwhile, the hydrostatic extrusion and indirect extrusion methods are also problematic in that the treatment of a pressure transmission solvent is not easy, an extruder is large-sized and high-priced, the maintenance cost of the extruder is high, and the operation method thereof is complicated, so the efficiency of a work is reduced, thereby causing the unit cost of a bus bar to increase.